Alcatel MainStreet 2902, Manual

Page: 136 / 344

13 — System timing and timing sources
13-4 2902 MainStreet Technical Practices
90-2906-01 May 2002
Timing sources can be configured for:
•
type of synchronization
•
class number
•
failure threshold
•
failure recovery
When the timing sources have been configured and timing has been enabled, the
2902 MainStreet system automatically generates its own map of all timing sources.
Each time a configuration change occurs (for example, when a new 2902 MainStreet
node is brought on-line or a timing source is reconfigured), the map is updated.
Each timing source is assigned a class number. The class number rates a source's
preference. When assigning a class number, consider factors affecting the timing
source's accuracy, reliability, and so on (which, in turn, depend on the node, the
network and the timing sources available).
Unless a timing source is specifically selected manually, the 2902 MainStreet system
automatically selects the source with the highest preference as its timing source. If
several sources in a network have the same preference, the node selects the source
that is the fewest number of hops away. A hop is a link between two pieces of
network equipment.
Current source failure
When the current timing source is lost (for example, due to a node or a link failure),
the node switches to free-run operation for approximately 10 seconds. During this
interval, the node determines if there is an alternate path to the master source of
synchronization. If an alternate path is available, the node synchronizes to that link.
If no path is available, the nodes determine the timing source with the highest
preference (lowest class number) among the sources that are ready and all nodes
synchronize to it.
If all sources fail or if the class numbers of all sources and nodes remain in the default
state, the network synchronizes to the internal clock of the active node with the
lowest node number.
Displaying timing sources
You can display the current configuration and status information for both timing
sources by entering:
CONFIG — SYNCH
Figure 13-1 shows the display. If the sources have not yet been configured, the
default settings are displayed.
Note —
After a database configuration has been restored, all
synchronization sources are unavailable to the system.